The decent into war in 1914 had very little to do with the assassination of Archduke Franz Ferdinand.

To many, it seems that the outbreak of World War One, beginning with the Austro-Serbian declaration of war in July 1914, was as a direct result of the assassination of Archduke Franz Ferdinand one month prior by Serbian Nationalists. However, by this point in time, war between the Great Powers of Europe was inevitable, and the assassination only acted as a catalyst for war; it was seemingly German aggression at this time that resulted in the decent into war, and this was something that had been growing far earlier than 1914.
During July 1914, there was surprisingly very little reaction from the Austro-Hungarians. Things only began to progress after the German promise of a "Blank Cheque" on 5th July, with Austria-Hungary sending an ultimatum for war to Serbia just over a week afterwards. This was not just a goodwill gesture on the part of the Germans; they felt a need to consolidate their position in the international arena by maintaining their one remaining ally (a relationship strengthened after Germany was vilified in the Moroccan Crisis a few years prior). The main reason for this actions, aside from their alliance, was a German fear of encirclement by the Entente powers; they wanted a preemptive war before Russia became a military power too strong for even German military might, so they pushed quickly for war with Serbia. They wanted this in particular, as if Serbia were to become involved in a war with their old colonial rivals, then Russia, as the so-called 'Protector of the Slavs', would feel the need to support their own ally, giving Germany the perfect opportunity for a preemptive war. War at this time, is engaged in quickly, would allow Germany to enact the Schlieffen Plan, which set out the plan to attack France through Belgium and then a quick mobilisation towards Russia once the French were defeated. As is evident of the war plans, Germany was eager for war, indicating that if the assassination had not occurred, they would have just waited for another crisis to act upon in their attempt to gain greater authority in Europe. The assassination was an opportunity taken, but actually the war itself had little to do with avenging an assassination as it did broader international power.